The present invention relates generally to the field of electric utility meters. More particularly, the present invention relates to both electronic watthour meters and meters utilized to meter real and reactive energy in both the forward and reverse directions.
Techniques and devices for metering the various forms of electrical energy are well known. Meters, such as utility power meters, can be of two types, namely, electro-mechanical based meters whose output is generated by a rotating disk and electronic based meters whose output component is generated electronically. A hybrid meter also exists, wherein an electronic register for providing an electronically generated display of metered electrical energy has been combined, usually optically, to a rotating disk. Pulses generated by the rotating disk, for example by light reflected from a spot painted on the disk, are utilized to generate an electronic output signal.
It will be appreciated that electronic meters have gained considerable acceptance due to their increasing reliability and extended ambient temperature ranges of operation. Consequently, various forms of electronic based meters have been proposed which are virtually free of any moving parts. In the last ten years several meters have been proposed which include a microprocessor.
Testing of electronic meters has always been a problem. A special mode of register operation known in the industry as the test mode has been available to ease register testing, however, little has been done to improve overall meter testing. Electronic meters have the potential of providing faster test times, multiple metering functions and calibration of the meter through software adjustment. However, implementing such functions can be expensive and complicated.
Presently, electric utility companies can test mechanical meters with a piece of test equipment which can reflect light off a metered disk to detect a painted spot as the disk rotates. An alternative form of testing mechanical meters is disclosed in U.S. Pat. No. 4,600,881xe2x80x94LaRocca et al. which describes the formation of a hole in the disk. A light sensitive device is placed in a fixed position on one side of the disk. As the disk rotates, and the hole passes over the light sensitive device, a pulse is provided indicating disk movement.
Since electronic meters preferably do not contain rotating disks, such simple testing techniques cannot be utilized. Consequently, a need exists for an electronic meter having a relatively simple means of testing the meter.
The previously described problem is resolved and other advantages are achieved in an apparatus for metering electrical power comprising a first processor which receives analog voltage and current signals and converts the analog voltage and current signals to respective digital voltage and current signals, a second processor which receives the energy signal and converts an energy signal into energy usage data, and a non-volatile memory coupled to the second processor for storing calibration constants and energy formula associated with a plurality of meter forms, such that some of the energy formula and calibration constants are downloaded from the non-volatile memory to the second processor. The first and second processors cooperate to determine the energy usage data based on the energy formula and calibration constants downloaded to the second processor, and the apparatus measures at least one of real power, reactive power, and apparent power based on energy formula and calibration constants associated with the plurality of meter forms. In addition, the first processor processes the digital voltage and current signals to generate the energy signal representative of a quantity of power and the second processor provides control functions within the apparatus. Further, the analog voltage signals are received by a resistive divider network and the current signals are received by a current transformer.
In accordance with a feature of the present invention, the second processor is configured to alter functions performed by the first processor, and the non-volatile memory may be an electrically erasable programmable read only memory.
In accordance with another feature of the present invention, the second processor includes an associated memory comprising a data memory coupled to the non-volatile memory for storing data downloaded from the non-volatile memory, and a program memory coupled to the non-volatile memory for storing program data for use with at least one of the plurality of meter forms to determine the electricity measurements. The associated memory may further comprise a read only memory for storing program data that is common to substantially all electricity measurement processing carried out by the apparatus independent of any one of the plurality of meter forms. For example, at least one Kn value may be stored in the non-volatile memory, where the one Kn value is downloaded to the associated memory and used by the second processor to generate output signals for any of real power, apparent power, and reactive power.
In accordance with yet another feature of the present invention, the apparatus may further comprise a communications interface connected to the second processor, such that the operation of the second processor is modifiable through the communications interface. The communications interface may be one of an optical port and an option connector.
In accordance with still another feature, the second processor controls operations of the apparatus in accordance with the configuration information, such as event timing and power management operations of the apparatus. Further, the operations may include a reset routine and a main routine, wherein the reset routine comprises a restoration function, an output device testing operation, a downloading operation from the non-volatile memory to the second processor, and self-test subroutines, and wherein the reset routine is initiated when the second processor receives a predetermined signal and the main routine comprises a time-of-day routine, a self-reprogram routine, boundary tasks, a season change determination routine, a display update routine, a communication scheduling operation, and an error determination routine.
According to another aspect of the present invention, an apparatus for metering electrical power is provided which comprises at least one processor which receives analog voltage and current signals and converts the analog voltage and current signals into energy usage data, the at least one processor providing control functions within the apparatus, and a non-volatile memory coupled to the second processor for storing calibration constants and energy formula associated with a plurality of meter forms, at least some of the energy formula and calibration constants being downloaded from the non-volatile memory to the at least one processor. The at least one processor determines the energy usage data based on the energy formula and calibration constants downloaded to the associated memory, and wherein the apparatus measures at least one of real power, reactive power, and apparent power based on energy formula and calibration constants associated with the plurality of meter forms.
According to a feature of the present invention, the apparatus further comprises a resistive divider network and a current transformer operatively connected to the at least one processor, wherein the analog voltage signals are received by the resistive divider network and the current signals are received by the current transformer.
According to another feature of the present invention, the at least one processor controls event timing and power management operations of the apparatus by executing a reset routine, wherein the reset routine comprises a restoration function, an output device testing operation, a downloading operation from the non-volatile memory to the second processor, and self-test subroutines, and wherein the reset routine is initiated when the second processor receives a predetermined signal. The at least one processor additionally executes a main routine which comprises a time-of-day routine, a self-reprogram routine, boundary tasks, a season change determination routine, a display update routine, a communication scheduling operation, and an error determination routine.